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J W MOORE

Publications and source records attributed to J W MOORE.

At least 19 recordsLinked to original sources
PubMed1964

TETRODOTOXIN BLOCKAGE OF SODIUM CONDUCTANCE INCREASE IN LOBSTER GIANT AXONS.

Previous studies suggested that tetrodotoxin, a poison from the puffer fish, blocks conduction of nerve and muscle through its rather selective inhibition of the sodium-carrying mechanism. In order to verify this hypothesis, observations have been made of sodium and potassium currents in the lobster giant axons treated with tetrodotoxin by means of the sucrose-gap voltage-clamp technique. Tetrodotoxin at concentrations of 1 x 10(-7) to 5 x 10(-9) gm/ml blocked the action potential but had no effect on the resting potential. Partial or complete recovery might have occurred on washing with normal medium. The increase in sodium conductance normally occurring upon depolarization was very effectively suppressed when the action potential was blocked after tetrodotoxin, while the delayed increase in potassium conductance underwent no change. It is concluded that tetrodotoxin, at very low concentrations, blocks the action potential production through its selective inhibition of the sodium-carrying mechanism while keeping the potassium-carrying mechanism intact.

Action Potentials↗
PubMed1964

EFFECT OF ETHANOL ON THE SODIUM AND POTASSIUM CONDUCTANCES OF THE SQUID AXON MEMBRANE.

The effects of ethanol on squid giant axons were studied by means of the sucrose-gap technique. The membrane action potential height is moderately reduced and the duration sometimes shortened by ethanol in sea water. Voltage clamp experiments showed that ethanol in sea water reduced the maximum membrane conductances for sodium (g'(Na)) and potassium (g'(K)). In experiments with multiple application of ethyl alcohol to the same spot of membrane, a reduction of g'(Na) to 82 per cent and of g'(K) to 80 per cent of their value in sea water was brought about by 3 per cent ethanol (by volume) while 6 per cent caused a decrease of g'(Na) to 59 per cent and of g'(K) to 69 per cent. Ethanol has no significant effect on the steady-state inactivation of g(Na) (as a function of conditioning membrane potential) or on such kinetic parameters as tau(h) or the time course of turning on gi g(Na) and g(K). It is concluded that ethanol mainly reduces g(Na) and g(K) in the Hodgkin-Huxley terminology.

Action Potentials↗
PubMed1962

Membrane potentials of the lobster giant axon obtained by use of the sucrose-gap technique.

A method similar to the sucrose-gap technique introduced be Stäpfli is described for measuring membrane potential and current in singly lobster giant axons (diameter about 100 micra). The isotonic sucrose solution used to perfuse the gaps raises the external leakage resistance so that the recorded potential is only about 5 per cent less than the actual membrane potential. However, the resting potential of an axon in the sucrose-gap arrangement is increased 20 to 60 mv over that recorded by a conventional micropipette electrode when the entire axon is bathed in sea water. A complete explanation for this effect has not been discovered. The relation between resting potential and external potassium and sodium ion concentrations shows that potassium carries most of the current in a depolarized axon in the sucrose-gap arrangement, but that near the resting potential other ions make significant contributions. Lowering the external chloride concentration decreases the resting potential. Varying the concentration of the sucrose solution has little effect. A study of the impedance changes associated with the action potential shows that the membrane resistance decreases to a minimum at the peak of the spike and returns to near its initial value before repolarization is complete (a normal lobster giant axon action potential does not have an undershoot). Action potentials recorded simultaneously by the sucrose-gap technique and by micropipette electrodes are practically superposable.

Action Potentials↗
PubMed1962

Current-voltage relations in the lobster giant axon membrane under voltage clamp conditions.

The sucrose-gap method introduced by Stämpfli provides a means for the application of a voltage clamp to the lobster giant axon, which responds to a variety of different experimental procedures in ways quite similar to those reported for the squid axon and frog node. This is particularly true for the behavior of the peak initial current. However, the steady state current shows some differences. It has a variable slope conductance less than that of the peak initial current. The magnitude of the steady state slope conductance is related to the length of the repolarization phase of the action potential, which does not have an undershoot in the lobster. The steady state outward current is maintained for as long as 100 msec.; this is in contrast to a decline of about 50 per cent in the squid axon. Lowering the external calcium concentration produces shifts in the current-voltage relations qualitatively similar to those obtained from the squid axon. On the basis of the data available, there is no reason to doubt that the Hodgkin and Huxley analysis for the squid giant axon in sea water can be applied to the lobster giant axon.

Action Potentials↗
PubMed1961

Electronic measurement of the intracellular concentration and net flux of sodium in the squid axon.

A unique, rapid, and non-destructive determination of the intracellular sodium concentration of a squid axon may be provided by the "voltage clamp" technique, in which the potential across the axon membrane is under electronic control. The potential at which the early component of ionic current reverses following a membrane potential step was used as an index of the intracellular sodium concentration. Several types of experiments were used to test the applicability of this method for measurement of intracellular sodium and its net flux. The concentration was found to increase from 38 mM for a fresh axon to 50 mM in about an hour. From this change, the net flux for a fresh resting axon was estimated to be 40 pmoles/cm(2) sec. Rapid stimulation of an unclamped axon produced a marked increase in the rate of sodium accumulation. Rapid pulsing of the membrane in a voltage clamp to potentials more positive than the sodium potential moved sodium out fast enough to produce a definite decrease in internal concentration. The agreement between the results with this method and those with more direct methods is quite satisfactory. An attractive feature of this method of intracellular sodium determination is that the physiological function of the axon is maintained and other measurements may be made concurrently.

Animals↗
PubMed1961

Action of external divalent ion reduction on sodium movement in the squid giant axon.

Voltage clamp measurements of the sodium potential have been made on the resting squid giant axon to study the effect of variations in external divalent ion concentration upon net sodium flux. From these measurements the intracellular sodium concentration and the net sodium inflow were calculated using the Nernst relation and constant activity coefficients. While an axon bathed in artificial sea water shows a slow increase in internal sodium concentration, the rate of sodium accumulation is increased about two times by reducing external calcium and magnesium concentrations to 0.1 times their normal values. The mean inward net sodium flux increases from a mean control value of 97 pmole/cm(2) sec. to 186 pmole/cm(2) sec. in low divalent solution. Associated with these effects of external divalent ion reduction are a marked decrease in action potential amplitude, little or no change in resting potential, and a shift along the voltage axis of the curve relating peak sodium conductance to membrane potential similar to that obtained by Frankenhaeuser and Hodgkin (1957). These results implicate divalent ions in long term (minutes to hours) sodium permeability.

Action Potentials↗